Synthetic absorbable polyesters are well known in the art. The terms absorbable, bioabsorbable, bioresorbable, resorbable, biodegradable are used herein interchangeably. The open and patent literature particularly describe polymers and copolymers made from glycolide, L(−)-lactide, D(+)-lactide, meso-lactide, epsilon-caprolactone, p-dioxanone, and trimethylene carbonate.
Medical devices in the form of polymeric films or a composite structure containing a substrate and a laminated film are known in the art and have utility in a variety of surgical applications including tissue repair, hernia repair, organ repair, etc.
Absorbable films and processes for forming such films from bioabsorbable polymeric materials have also been described by various researchers over the years, e.g., U.S. Pat. No. 7,943,683 B2, “Medical Devices Containing Oriented Films of Poly-4-hydroxybutyrate and Copolymers”; U.S. Pat. No. 8,030,434 B2, “Polyester Film, Process for Producing the Same and Use Thereof”; U.S. Pat. No. 4,942,087A, “Films of Wholly Aromatic Polyester and Processes for Preparation Thereof”; U.S. Pat. No. 4,664,859A, “Process for Solvent Casting a Film”; and, U.S. Pat. No. 5,510,176A, “Polytetrafluoroethylene Porous Film”. Various conventional methodologies and processes are known and exist to produce polymeric films. They include, but are not limited to, melt extrusion, solvent casting, and compression molding. However, not all polymers can be easily converted to film products; additionally, different conversion techniques have different challenges. In the case of melt extrusion, the resin must be thermally stable, exhibiting an appropriate melt viscosity, i.e., not too low so as to cause “dripping” and not too high so as to develop excessively high pressures in the extruder, causing instability and non-uniform results. In the case of resins possessing low glass transition temperatures, the dimensional stability of the films made therefrom may be very low if the polymer morphology includes some chain orientation. This is a great driving force for shrinkage and distortion. To circumvent dimensional instability difficulties, the development of a certain amount of crystallinity in the film is advantageous. The rate of crystallization is important in establishing a robust film extrusion process, while the overall level of crystallinity is important in achieving dimensional stability and good mechanical properties. It is known that a crystallinity level that is too low will result in films which may distort upon ethylene oxide sterilization or upon exposure to even mildly elevated temperatures during processing, transportation, or storage. In certain surgical applications, it is desirable for the final films to be strong with appropriate tear resistance, yet pliable enough to possess good handling characteristics. Examples of such surgical applications include hernia film-containing repair patches requiring suturing and/or tacking as a means of fixation to the surrounding tissues, various film-based medical devices that undergo extensive handling and manipulation prior to implantation, in cases where the film is a load-bearing component, etc.
An absorbable polymer used to manufacture films must possess certain melt and thermal properties, certain crystallization characteristics, as well as certain mechanical and hydrolysis properties, if it is to be suitable for fabricating surgical film products by a melt extrusion process. In the case of films made by solution casting, the polymer resin needs to possess appropriate solubility in a suitable solvent. Suitable solvents advantageously have an appropriate vapor pressure curve leading to suitable evaporation rates, and are generally non-toxic. The polymer must then possess certain solubility and crystallization characteristics, as well as certain mechanical and hydrolysis properties, if it is to be suitable for fabricating surgical film products by a solvent casting process.
Methods of laminating a polymeric film on different substrates have been described in the patent literature. For instance, U.S. Pat. No. 8,349,354B2 (Andjelic) describes a hemostatic composite structure having an absorbable fabric or non-woven substrate and continuous non-porous polymeric film that is laminated on one major surface of the substrate. However, the film layer is limited to an amorphous polymeric material, or semi-crystalline polymeric material having a melting point temperature below 120° C.
For the lamination of polymeric films having a melting point temperature significantly higher than 120° C. (e.g., around 200° C.), different approaches have been used and disclosed in the prior art, including the addition of an adhesive layer between the high melting point polymeric film and a substrate as described in U.S. Pat. No. 7,615,065 and U.S. Pat. No. 8,821,585 B2. In the market place, the ETHICON PHYSIOMESH™ mesh device is a commercially available hernia mesh product that is made from an absorbable polymer film (based on 75/25 Gly/Cap resin) coupled with a non-absorbable polypropylene mesh. To join the high melting point polymeric film onto the mesh, an interlayer of lower melting point poly (p-dioxanone)-based film (melting point of 110° C.) is used on both sides of the mesh to glue these three structures together to form the composite structure. If no adhesive layer/film were used for bonding, a high temperature above 150° C. would be needed to bond the absorbable polymer film to the mesh, resulting in distortion and shrinkage of the mesh. On the other hand, the presence of an additional layer for bonding purposes increases the risk of adverse tissue reactions (more degradation products released such as free acids), biocompatibility, and increases device stiffness; it also significantly increases production cost and complicates the manufacture of such a medical device.
Similar to the technology mentioned above, U.S. Pat. No. 3,467,565A describes the lamination of a high melting plastic film, such as Nylon, onto a carrier web using a low melting plastic film, such as polyethylene. The disclosure is silent with respect to using this technology on absorbable polymer systems.
A method for forming strong cross-laminated flat films described in U.S. Pat. No. 4,475,971A comprises composite, coextruded film structures having a higher melting point layer and a lower melting point layer. The higher melting point layer may be polyethylene, nylon, polyester or polypropylene, while the lower melting point component is selected from the group consisting of an ethylene/vinyl acetate copolymer, a low density polyethylene polymer and an ethylene/propylene copolymer. Again, the low melting point component as a glue is used on all non-absorbable components.
U.S. Pat. No. 6,911,244B2 describes the encapsulated barrier for flexible films comprising a barrier layer made from a thermally sensitive material, preferably ethylene vinyl alcohol, and at least one substrate, preferably oriented polypropylene encapsulated by two or more adhesive layers. The adhesive layers, in addition to having a bonding function may also protect the barrier material from high temperatures of the hardware and long residence times within the hardware.
US 20130001782A1 teaches a method utilizing a low melting thin metallic film for lamination of a high melting point soldering layer on a three-layered structure for fabrication of a semiconductor device.
A biodegradable mesh and film stent for use in blood vessels is described in U.S. Pat. No. 5,629,077 comprising a sheet of a composite mesh material made from biodegradable high strength polymer fibers bonded together with a second biodegradable adhesive polymer, and laminated on at least one side with a thin film of a third biodegradable polymer. The lamination is achieved by heat bonding via a lower temperature adhesive biodegradable layer, such as epsilon-caprolactone or a low melting point temperature plurality of fibers in a mesh structure.
Laminated food packaging having a multilayered film structure and having low vapor and gas permeability is described in U.S. Pat. No. 3,932,693A. The structure comprises a base layer of an oriented polypropylene film laminated onto a layer of a vinylidene chloride polymer using a layer of ethylene/vinyl acetate copolymer film having vinyl acetate content greater than 10 percent by weight.
U.S. Pat. No. 4,119,481A describes a fusion laminated high-temperature fabric made of amorphous silica fibers with a thermoplastic film made from vinyl, polyester or urethane polymers using high energy infra-red radiation. The high energy is preferentially absorbed in a short time and space resulting in an increase in temperature sufficient to produce the desired degree of adhesion with the thermoplastic film. Although this method of lamination does not require an additional adhesive element, the use of high energy radiation can cause degradation in cases where fabric and/or film are made from absorbable polymers.
A method of making laminated Nylon-based fabrics is described in U.S. Pat. No. 2,269,125A. The method provides for treating the fabric with water for easier heat pressure bonding. The absorbed moisture lowers significantly the glass transition temperature and increases thermal conductivity of Nylon-based fibers allowing for the lower lamination temperatures. However, the use of moisture with heat on absorbable polymer structures would cause significant polymer degradation.
In summary, there is a strong, continuing need in this art for novel methods that will effectively laminate high melting temperature, semi-crystalline absorbable films on various thermally sensitive absorbable or non-absorbable substrates without the need for any additional adhesive layer or any type of glue substance, including moisture. The lamination of thermally sensitive substrates needs to be conducted using low lamination temperatures, such as 120° C. or lower, to avoid chemical degradation and physical distortions and novel methods are needed to provide for the lamination of such substrates.